Halogen-containing alumina catalysts are used for the alkylation of alkanes with olefins to produce high octance gasoline blending components and for the isomerization of hydrocarbons. These catalysts have also been suggested for the polymerization of olefins. They can be prepared by contacting alumina materials with various halogen-containing reagents. Calcined aluminas are generally used as starting material, but halogenation of uncalcined alumina prior to calcination has also been suggested. Various halogen-containing reagents may also be used, such as chlorine or bromine or their mixtures with chlorinated derivatives of low molecular weight hydrocarbons. Methods for preparing these catalysts are disclosed in U.S. Pat. Nos. 2,479,110; 2,642,384; 3,240,840; 3,523,142; 3,549,718; 3,646,152; 3,689,434; 3,702,293; 3,702,312 and 4,083,800.
However when employed for polymerizing olefins, these alumina catalysts yield only lower molecular weight polymers. Moreover, when used for polymerizing feeds comprising mixed butenes, these catalysts give copolymers containing large amounts of poly-n-butenes and small amounts of polyisobutenes.
Liquid polyolefins are now employed as additives in lubricating oils, insulating oils or even as substituents for lubricating oils. But, these liquid polyolefins must have a molecular weight higher than the dimers and trimers. For example, liquid polyisobutenes of formula (C.sub.4 H.sub.8).sub.n where n usually lies between about 5 and 70 are particularly required for these uses.
There is, therefore, a need for a catalyst allowing to obtain liquid polyolefins having a molecular weight higher than the trimers. There is also a need for a catalyst which allows the selective polymerization of isobutene from a feed containing mixed butenes, with formation of liquid polymers.